1. Field of the Invention
The present invention is generally related to communication systems. More particularly, the present invention is related to cable modem systems and methods for transferring data.
2. Background
In conventional cable modem systems, a hybrid fiber-coaxial (HFC) network provides a point-to-multipoint topology for supporting data communication between a cable modem termination system (CMTS) at the cable headend and multiple cable modems (CM) at the customer premises. In such systems, information is broadcast downstream from the CMTS to the cable modems as a continuous transmitted signal in accordance with a time division multiplexing (TDM) technique. In contrast, information is transmitted upstream from each of the cable modems to the CMTS as short burst signals in accordance with a time division multiple access (TDMA) technique. The upstream transmission of data from the cable modems is managed by the CMTS, which allots to each cable modem specific slots of time within which to transfer data.
Conventional cable modem systems are asymmetrical in that there is considerably less bandwidth available for upstream transmissions than there is for downstream transmissions. This lack of upstream bandwidth is further exacerbated by the fact that the upstream channels must be shared by multiple cable modems. As a result, the conservation of upstream bandwidth is imperative in order to maintain overall system performance. This is particularly true where cable modem users are engaging in activities that require both substantial upstream and downstream bandwidth, such as IP telephony, video teleconferencing, and Internet gaming.
Several industry standards or protocols have evolved to address these concerns. Conventional cable modem systems utilize equipment and protocols that are compliant with the Data Over Cable System Interface Specification (DOCSIS) to carry out the transfer of data packets between multiple cable modems and a CMTS. The term DOCSIS generally refers to a group of specifications published by CableLabs that define industry standards for cable headend and cable modem equipment. In part, DOCSIS sets forth requirements and objectives for various aspects of cable modem systems, including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for data over cable systems. The most current version of DOCSIS is DOCSIS 1.1.
One technique specified by DOCSIS to conserve upstream bandwidth involves Payload Header Suppression (PHS). PHS, as defined by DOCSIS 1.1, allows the suppression of unnecessary Ethernet/IP header information in the payload of a DOCSIS packet by the cable modem and subsequent reconstruction of the header by the CMTS. The goal of PHS is to reduce the number of bits transferred per packet, thereby improving network bandwidth utilization. However, DOCSIS PHS (DPHS) only permits header suppression based on the presence of redundant header bytes in sequentially transmitted packets.
What is needed is a flexible and efficient payload header suppression technique that addresses the above-identified concerns.